Electron discharge i



Aug. 11, 1959 v J. D. M GEE 2,899,576

' ELECTRON DISCHARGE DEVICES Filed March 25, 1957 United States Patent) Thisiiiventi'on relates to el'ect'rorrclicliargedevices-antl I particularly to photo-electric tubes having" a photocathodeand eiectrodes which are man'rtained at a high potential relati vely to one another.

The formation of a photo-sensitive surface must of necessity-be" carried out-"after the electrodes have been introduced intoa vessel and thevessellevacuated. 'I-he most sensitive typesof' photo-ca-thodesurfaces inclnde' caesium in their composition. Normally, this-caesium is introdnced into the-vessel'in the-fcrmof vapour which condenses on and reacts with-a-base metal,- for example ysoff the} cathode-10* formdthe' r is a metalhmember' sealed into the glass vesseli and sensitive surfacer a If other electrodes are: also exposed to' the caesium vapom'; condensation will. occur onthesm electrodestzasr well as on the: cathode and similar reaction of the caesium with the base metal: may: occur: Theiresultanti surface: has: a low workefunctionandi electrons: may be: drawn from theisnrface dueitoithe :high potential ielectricl fielttpresentrinioperation'ofthe device;

a eflect: limits the maximumtvoltage which can be;

applied-roan photo-electric tube; and: hence. the useful-z 1 known type so thatithesegarts andatheii operation overall; gainsof amimage; intensifier The caesium vapour may also result. in positive:

caesium ions in operation, which drift back to the photo- 40 cathode there liberating more electrons These spurious 'electrons: are accelerated towards the anode and,tin an image converting device, cause a rapid risei'in background illumination, with consequent loss of contrast; i

111i? object ofthe present invention is to provide" a novel method" of'coating' and mountinga condensation coated electrode in an electron discharge device so that condensation of the vapour on other electrodes is substantially avoided.

Another object of the invention is to provide an electron discharge device having a condensation coated electrode in which other electrodes are not contaminated by the vapour so that, in the case of an image intensifier for example, with a photo-cathode formed by vapour condensation, it is possible to attain a much greater brightness intensification.

According to the invention, an electron discharge device comprises a vessel having first and second chambers connected by way of an aperture, the first chamber containing at least one electrode and the second chamber being adapted for the admission of vapour thereto, the device also comprising an electrode coated while inside the vessel by vapour condensation thereon and adapted to occupy first and second alternative positions, the first serving to close the said aperture during the coating operation and the second being in operative relationship to the electrode or electrodes in the first chamber.

A method according to the invention makes use of a vessel for the electron discharge device which is shaped to have first and second chambers connected by way of an aperture and the said method comprises arranging Patented Aug. 11, 1959 ice 1i closes the; aperture admitting; vapour into thesecqnd;

chamber so. that, condensation occurs; :on, a; faceloithet electrode: and subsequently arranging-aha,- electrodfitintai.

second position in which theacoatedsurfacefacesg-intq, the, first. chamben whereby vapour is substantially excluded from, the; first, chamberduring; the. coating; operation. 1

Most conveniently, the. coated electrcde.is;.he1d in;

0 position for: coatinggandtthen heldginzitsoperativetposie tion by at least one magnetically releasable catch. y

In order that the invention may be readily carriedjnto efiect, one. embodiment, will, now be particularly de scribed, by way ofexample, with referenceto-thetaccom-tpanying}; drawings, ofiiw hichzj v p g Figure 1 shows an'imagelintensifiertubetarrilngfiifotl operation and t i F u -2 illustrates ee asa r ngthe manufacture at. the. tube, 'partonly of the,v tubeof, Figure .1. being shown... ln Eigure 11 the. image. intensifier tube'is: constructed inlalvessellahaving a firstchamb rl wh ch isthe world,

' ing,;section of. the;- tube..and. a..'second7 chamber 3, which v is a processing section uscdlduring. thetformation of, at. photosensitive surface, 62011 a, surface, of atcathodeplate 4. Thechambers. 2, 3 ofithe vesselil are. connectedjby way of :an, aperture. ina member, sfwhich, ,il'i'tlltis.v example havingan inwardly extending; annular flange- I Alternatively, the; 'apcnuredfmemher may. be Candace" tivelytcoatedr Asshow-IL in; Figurel; the plate 4- is arran d with photor-sen'sitivelsurfaceGficiflgihtq the hamberl-g The not be. further described;

cathode plate 4Iijst a. circular plate which, prior to cqatiilg, is arranged against the flange 5 so asto close oftlie chamber 21 The abuttingsurfaces' of'thegplate andthe flange. are coated with colloidah graphite; The: plate'f lf is held securely'in this. position by c atches9"ol:, magnetic material wliich are spring'loaded by coilsprings lfiffandi' arranged in" obliquely inclined side tnbes 'jlli tamination of the electrodes 7 and screen 8 is thereby avoided.

After suitable heat treatment to form the photosensitive, surface 6, the complete vessel is sealed ofi at the exhaust tube 12.

The catches 9 are released by manipulating magnets 13 outside the vessel 1 so as to draw back the catches 9 against the springs 10, as shown in Figure 2.

By careful shaking of the tube, the plate 4 is moved away from the flange 5, turned over and replaced on the flange 5 so that the coated surface 6 now faces into the chamber 2. The magnets 13 are removed so that the catches re-engage the plate 4 thus holding the photocathode in the position shown in Figure 1.

In this position, an electrical connection is made to the photo-sensitive surface 6 by way of the conducting flange 5. A lead 14 is connected to the flange 5 and taken out through a seal 15.

fWhen the tube is arranged for operation, it is provided with a conventional electron lens such as the solenoid 16 An optical image is projected on the photo-sensitive surface 6 by a lens system 17 and an electron image is pro duced on the fluorescent screen 8. V a I While the invention has been described with'reference to a simple high voltage image intensifier, by way of example, it is not restricted to this type of tube and may be applied to multi-stage image intensifier tubes and in the image intensification section of television pick-up tubes. e

I claim: 1. An electron discharge device comprising a vessel having first and second chambers connected by way of an aperture, the first chamber containing at least one electrode and the second chamber having entry means for the admission of vapour thereto, the device also comprising an electrode coated while inside the vessel by vapour condensation thereon and adapted to occupy first and second alternative positions, the first serving to close the said aperture during the coating operation and the second.

being in electrically operative relationship with the electrode or electrodes in the first chamber.

' 2. An electron discharge tube comprising a vessel containing an electrode to be coated by condensation of V vapour thereon and at least one electrode upon which the condensation of the said vapour is to be avoided, in which the vessel has first and second chambers connected by way of an aperture, the electrode or electrodes upon which condensation is to be avoided being arranged wholly in the first" chamber, the second chamber having entry means for the admission of the vapour thereto and the electrode to be coated being adapted to close the said aperture while presenting a surface to vapour in the second chamber during the coating operation and subsequently to be movable to a second position in' which the said surface faces into the first chamber.

3. A method of coating and mounting an electrode for an electron discharge device including a vessel having first and second chambers connected by way of an aperture, comprising arranging said electrode in a first position in which it closes the aperture, one surface of the electrode cylindrical, being substantially rectangular in longitudinal section, and is divided into first and second chambers by aconductive annular flange arranged intermediately of the ends of the vessel, and the electrode is a circular disc.

6. A device as claimed in claim 2 in which the vessel is V cylindrical, being substantially rectangular in longitudinal section, and is divided into first and second chambers by a conductive annular flange arranged intermediately of the ends of the vessel, and the electrode is a circular disc.

7. A device as claimed in claim 5 in which the electrode is held in its first and second positions by at least one releasable catch.

8. A device as claimed in claim 2 in which the electrode is held in its first and second positions by at least one releasable catch.

9. A device as claimed in claim 7 in which the coated electrode is the photo-cathode of an image intensifier tube, the associated electrodes and screen being arranged in the first chamber of the vessel.

10. An electron discharge tube comprising a vessel containing an electrode to be coated by condensation of caesium vapour thereon to form a photocathode and at least one electrode upon which the condensation of the said vapour is to be avoided, in which the vessel has first and 1 second chambers coated by way of an aperture, the electrode or electrodes upon which condensation is to'be avoided, being arranged wholly in the first chamber, the second chamber having entry means for the admission of vapour thereto and the electrode to be coated being adapted to close the aperture while presenting a surface facing into the first chamber, admitting vapour into the second chamber, so that condensation occurs on the other face of the electrode and subsequently reversing the electrode from that position, so that the coated surface faces into the first chamber, whereby vapour is substantially to vapour in the second chamber during the coating operation and subsequently to be movable to a second position in which the caesium-coated surface faces into the first chamber.

References Cited in the file of this patent UNITED STATES PATENTS Henry Apr. 24, 1945 

